A documentary film is a movie that attempts, in some way, to document reality. Even though the scenes are carefully chosen and arranged, they are not scripted, and the people in a documentary film are not actors. Sometimes, a documentary film may rely on voice-over narration to describe what is happening in the footage; in other films, the footage will speak for itself. Often, a documentary film will include interviews with the people in the film.

The earliest film of any sort was a documentary film. These featured single shots of actual events, such as a boat leaving shore, and were referred to as "actuality" films. Other early forms of the documentary film included propaganda films, such as the famous Leni Reifenstahl movie, Triumph of the Will, which made Adolph Hitler appear heroic.

One type of documentary film that became popular in the 1950s was called cinema verité, which is the literal French translation of "cinema truth." Cinema verité is a type of documentary film that includes no narration; the camera simply follows the subject. One famous example of such a film is Don't Look Back a biography film about Bob Dylan, covering his tour of the United Kingdom in 1965.

In recent years, the documentary film genre has become more popular and high profile, though it is still far less popular generally than the action or adventure film genre. Many of today's examples of the documentary film have a political or otherwise controversial agenda, such as An Inconvenient Truth, Super Size Me, and Fahrenheit 911. Michael Moore's Fahrenheit 911, which documented the Bush family's ties to Saudi Arabia and Osama bin Laden, was the most popular documentary film of all time, with over $228 million US Dollars in ticket sales.

The documentary film is still low on the radar of most movie audiences, but the popularity of recent films illustrates that audiences are willing to watch a movie that has a serious agenda. Because documentary films are much cheaper to produce than commercial movies, they are a low risk for studios. In the future, we are likely to see many more documentary film releases in theaters.